On Feb 15, 2009, at 5:01 PM, Mark Engelberg wrote:
> > On Sun, Feb 15, 2009 at 1:44 PM, Chouser <chou...@gmail.com> wrote: >> (defn my-interpose [x coll] >> (loop [v [x] coll coll] >> (if (seq coll) ; Don't assume coll is a seq-or-nil >> (recur (-> v (conj (first coll)) (conj x)) (rest coll)) >> v))) > > > You know, there is an empty? predicate. Why not write it as: > (defn my-interpose [x coll] > (loop [v [x] coll coll] > (if (empty? coll) v ; Don't assume coll is a seq-or-nil > (recur (-> v (conj (first coll)) (conj x)) (rest coll))))) > > I know that your first version is viewed as more idiomatic in Clojure, > but I've never understood why Rich and others prefer that style. It > assumes that converting something to a seq is guaranteed to be a > computationally cheap operation, and I see no reason to assume that > will always be the case. I can certainly imagine seq-able > collections that take some time seq-ify, so converting to a seq to > test for empty, and then just throwing it away causing it to be > recomputed in rest doesn't seem as future-proof as just using empty?. > When walking a chain of seqs, empty? made no sense as there is no such thing as an empty seq. Now that rest returns a collection, this makes more sense (although still not my preference), but to each his own. Let's please not get bogged down in a style discussion now. You should be quite happy for this: (rest [1]) -> () ;an empty sequence, note - not a canonic/sentinel value! Also note empty? is still defined like this: (not (seq coll)) Rich --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "Clojure" group. To post to this group, send email to clojure@googlegroups.com To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en -~----------~----~----~----~------~----~------~--~---
